Pneumococcal sepsis with false-negative blood cultures

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Diagnostic Laboratory Science

Background:

• False-positive blood cultures due to contamination are common.
• Certain bacteria, like Streptococcus pneumoniae, may rapidly die in broth cultures, leading to false-negative results.
• False-negative blood cultures can delay diagnosis and treatment of serious infections.

Purpose of the Study:

• To investigate the phenomenon of false-negative blood cultures in patients with pneumococcal infections.
• To identify early indicators of bacterial growth in blood cultures that may be missed by standard 24-hour incubation.
• To alert physicians and laboratory personnel to potential pitfalls in blood culture interpretation.

Main Methods:

• Observation of patients with suspected pneumococcal infections and blood cultures.
• Monitoring blood culture bottles for visual cues such as hemolysis and methemoglobin formation.
• Performing blind subcultures at earlier time points (e.g., 12 hours) in addition to standard 24-hour subcultures.
• Utilizing counter-immunoelectrophoresis to detect pneumococcal antigen in blood culture broths.

Main Results:

• Several patients presented with pneumococcal infections but had false-negative blood cultures at 24 hours.
• Hemolysis and methemoglobin formation were observed within 12 hours, suggesting bacterial growth.
• Blind subcultures at 12 hours successfully identified pneumococci.
• Pneumococcal antigen was detectable via counter-immunoelectrophoresis even when 24-hour subcultures were negative.

Conclusions:

• False-negative blood cultures are a potential issue, particularly for Streptococcus pneumoniae.
• Early visual inspection of blood culture bottles for signs like brown sediment or hemolysis is crucial.
• Prompt subculturing based on visual cues can improve the detection of viable bacteria and aid in timely diagnosis.